Typical mobile communication systems have been developed to provide voice services while guaranteeing user mobility. Such mobile communication systems have gradually expanded their coverage from voice services through data services up to high-speed data services. However, as current mobile communication systems suffer resource shortages and users demand even higher-speed services, development of more advanced mobile communication systems is needed.
In existing mobile communication systems, only voice calls have been used as emergency calls. However, advances in packet networks and enormous popularization of smartphones have necessitated introduction of Non-Voice Emergency Services (NOVES) that enable a user equipment to place an emergency call with media other than, or in addition to, voice (NOVES call) in an emergency situation. For example, a user may desire to send a video clip showing the emergency situation to an emergency center or may desire to perform text communication with an emergency center if use of voice communication is difficult. In the present disclosure, a NOVES call may be a call with voice and other media or a call with media other than voice.
When a radio access technology (RAT) is changed owing to movement of a user equipment processing a NOVES call, the target network may support only a portion of media currently used by the user equipment. In this case, the network may have to select a portion of media to be transferred to the target network according to media preference information of the user. This is because preferred media may be different according to situations of the user. For example, the user may prefer video over voice in some cases.
For a normal call, media to be transferred to the target network may be selected on the basis of user preferences stored in the subscription data or operator policies. However, as an emergency call is a non-subscription service, the network cannot be aware of media preference information of a user. In addition, as user media preference information may change at each attempt to make an emergency call, it may be inflexible for the network to store user media preference as static information for later usage.